Okay, story time:
Had basically this same problem almost a year so I had Carmax look at it when I had my '08 Tahoe in the shop back in January. The AC would blow cold air on the driver side and hot air on the passenger side. Carmax replaced that blend door motor and said it was fixed.
Fast forward to this summer. It gets hot so I start using the AC again and still have the same problem, plus now the air will randomly start blowing through the defroster vent and no other vents. I try to switch it to blow at feet, at head, etc., and it never comes out of the correct vents. Apparently Carmax didn't get it fixed.
I dropped my Tahoe off for more work on June 27th and they checked it out and said that the problem must be with the AC module. It was giving them error codes so they decided to take the truck to a Chevy dealership to have it worked on.
Chevy does some sort of reset on the module and Carmax picks it up. On the way back, the Carmax driver realizes the AC is still not working so he turns around and takes it back to Chevy. Chevy decides to just replace the whole AC module.
I get a call from Carmax 20 minutes ago and he tells me the Tahoe was dropped off last night but he just checked and the AC is STILL not working correctly. Looks like it's back to Chevy for a FOURTH repair attempt.
I'm getting pretty frustrated because I've been without my baby for about 2 weeks now. I'll give the guy at Carmax credit though, because he seems pretty pissed at the Chevy dealership. He said he was going to have some words with the supervisors at Chevy and figure out what the hell is going on and why Carmax has spent so much money on it (covered under my warranty) without it being fixed.
But seriously, replaced blend door motor AND the AC module and it's still not working? I don't know much about how the AC system works, but what the hell else could it be?